The need for continuous duty, high power rotating anode x-ray tubes exists in medical radiography, i.e., fluoroscopy and computerized tomography (CT), and in industrial applications such as x-ray diffraction topography and non-destructive testing.
Liquid cooled rotating anode x-ray tubes are, in general, well known. In such x-ray tubes, a hollow anode is disposed so that a rotating portion thereof is irradiated by an energy beam (e.g., electron beam). The irradiated portion of the anode is generally referred to as the electron beam track. Substantially all of the heat generated by irradiation by the energy beam is transmitted to a heat exchange surface, typically the interior wall of the hollow anode underlying the electron beam track and adjacent areas. In other words, the heat exchange surface is generally an area of the interior surface of the anode larger than the electron beam track. A flow of liquid coolant is passed into contact with the heat exchange surface to remove the heat therefrom, and thus cool the anode.
It is also well known that a centrifugal force in the presence of a liquid cooled heat transfer surface that is cooled by nucleate boiling can increase the effective rate of heat transfer by the more efficient removal of nucleate bubbles. In prior art devices, however, only a single source of centrifugal force is utilized. More specifically, devices utilizing a curved heat transfer surface disposed on the interior of a hollow target, which rotates about a stationary, coaxially disposed septum to generate a centrifugal force, are known. In general, in such devices the coolant velocity vector and the curved heat transfer surface lie in the planes containing the line of the axis of anode rotation. The general flow of coolant is axial, that is, along the line of the axis of anode rotation, approximately radially up an input anode face, axially across the anode heat exchange surface, and then approximately radially down a discharge face of the anode, to be discharged axially along the line of the axis of anode rotation. The useful curvature of the heat exchange surface is concave and interacts with the flow of coolant such that a single centrifugal force proportional to the square of the relative tangential velocity between the coolant and curved surface is established on the curved anode surface.
It would be desirable to independently generate additional centrifugal forces to further enhance heat removal at the heat transfer surface. Independent control of each source of centrifugal force would facilitate optimization of system performance parameters while enhancing heat transfer.